In the field of filling machines where a liquid product is to be filled into a container at a high fill rate it is a commonly known problem how to ensure the quickest possible filling of the container at the smallest amount of splashing, after-dripping or foaming. Especially in containers which are to be heat-sealed after the filling operation, trapped liquid drops or foam bubbles may compromise the seal integrity. These problems are exacerbated by high filling speeds and a large distance between the product surface and the end of the filling pipe.
In the food packaging industry, where liquid foodstuffs are to be filled into a container which is later to be sealed, the liquid foodstuffs are usually delivered through a filling pipe with a rubber nozzle at its end. In one variant, the open end of the container to be filled is aligned with the rubber nozzle and moved by a lifter mechanism towards the rubber nozzle, such that it enters the inside of the container. The lifter mechanism is programmed to stop the movement of the container at a certain predefined distance from its initial, or lowermost position. At this predefined distance, the liquid foodstuff is poured from the nozzle into the bottom end of the container and the lifter mechanism moves the container downwards back to its initial position while the liquid foodstuff is filled into the container. Shortly before the container has reached its initial position the flow from the rubber nozzle is stopped. After reaching the final position, the vertical movement of the lift mechanism and thus the container is stopped. Thereafter, the container is moved to the sealing part of the machine. In some other variants, the filling nozzle moves instead of the container during the filling cycle.
Now, in order to be able to fill packages at the specified machine capacity, it is very important that the product is poured out from the filling nozzle in a controlled way so that the distance between the rubber nozzle, that is mounted at the lower end of the filling pipe, and the product level inside the package is essentially constant and numerically correct during the time the lifter mechanism is lowering the package. Usually, the lifter mechanism is synchronized in some way with a filling pump delivering the liquid foodstuff through the rubber nozzle. The product level seen from the machine point of view shall be close to constant (in space) during at least half of the filling time i.e. up until the time point when the lifter mechanism de-synchronizes from the filling pump.
In some known filling machines, such as the example shown in FIG. 1A a container is lifted up by a container lifter from a bottom rail to its highest position, so that the distance between the lowest part of the rubber nozzles and the inside bottom of the package is correct when the pump starts to deliver the product.
There is usually a defined recommended distance between the inside container bottom and the lowest point of the rubber nozzle. When filling “tricky” products like Soy milk this distance may not be optimal, resulting in trapped air bubbles, product splash and foam. The problem with the mentioned effects is that product residues often will contaminate the transversal sealing zones of the containers causing bad container integrity.
Other examples of such filling machines are given in the U.S. Pat. Nos. 4,108,221 and 6,941,981.
There are many causes to a non-satisfactory filling performance. One of them is the timing difference between opening and closing of the inlet and the outlet valves, which valves are provided to control the discharge of the product into the container. If there for example is a valve overlap (i.e. both the inlet and the outlet valves are opened at the same time) at the end of a pump delivery stroke then severe after-dripping will occur coming from the inside of the rubber nozzle. This after-drip has a high probability to hit the transversal sealing zone during indexing of the containers, i.e. during the time the containers are moved from one station of the packaging apparatus (of which the filling apparatus is a part) to another. If the valve overlap is in the beginning of the pump delivery stroke then too much product may come out too fast resulting in splashing that might end up on the outside of the rubber nozzles. This product could/will later create undesirable after-dripping.
Another cause for after-dripping is that the product has been splashing up on the outside of the rubber nozzles some time during the filling. This can happen directly at the start of filling when the first product hits the bottom of the package. It is also possible that bad synchronization between the container lifter and cam profiles of an associated product pump can make the rubber nozzle dip down into the product and thereby making the outside of the rubber nozzles wet. At the end of the filling, when the carton lifter desynchronizes from the pump and moves down to the bottom rail, the product that is in contact with the outside of the rubber nozzle will drip.
A third reason for product splashing up on the outside of the rubber nozzle is the so called distance filling that occurs when the pump has started to decelerate and the carton lifter just continues its move down towards the bottom rail. During this “distance filling” the product surface may be very rough and stormy. It is worse when the distance between the lowest part of the rubber nozzle and the rough product surface is larger i.e. this distance should be minimized for as long as possible.
It is worth mentioning that it is not only in the filling station that product residues may contaminate the transversal sealing zone. Examples of other machine functions that may cause product residues in the top seal area are the package transport, the hot air heating of the top seal area and the squeezing of the gable top. If the product surface is rough at the end of the filling then it is very likely that the slosh wave that is created will make product touch the sealing zone, likewise if foam has been created due to trapped air or if the distance between the rubber nozzle and the product surface is too large during the major part of the filling, this foam will lay on top of the slosh wave or be blown up on the transversal seal zone by the top heater or be blown out at the start of the top squeezer close motion.
To eliminate foam and splashes it is very important to have a very short distance between the ideal product surface and the rubber nozzle during the major part of the filling. With current solutions it is extremely hard to optimize this. Although manually adjusting the times when the inlet and outlet valves open to achieve an improved filling result may work for some products, for others it may however only be possible to make the nozzle distance “good” either at the start of the filling or at the end but not both, whereby one of the undesired effects described above may occur. For an optimal filling cycle, it is desirable to keep the distance between the product level in the container and the end of the rubber nozzle essentially constant throughout the filling cycle.